I was reading this paper by Cretekos et al (2008), in which they state that wing development in the bat is not complete until after birth - the wing continues to elongate postnatally. This would suggest that bats are unable to fly immediately after birth, and a brief web search confirms this.

However, I would like to know:

When is wing growth (by which I simply mean outward growth or extension) complete?

When are bats able to fly? (Are there other developmental processes that take place after wing extension that delay this process?)

1 Answer
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The ability of the forelimbs in bats (as well as in other tetrapods) to grow depends on the proliferation activity and ossification of cartilage in growing zones of the bones. Adult bats do not grow (as is the rule for mammals) and wing parameters (wing span and area) show growth curves with more or less pronounced plateau, which asymptotically leans to "adult" values. (This reflects progressive ossification of the cartilage.) As one could intuitively expect, variability in wing relative parameters decreases with age, meaning that juveniles before their first flights show more diversity in wing shapes than flying juveniles and those, in turn, approach gradually the narrow variability of these parameters of the adults.

Juvenile bats start performing their first short flights even before weaning. The main requirement for the flight ability per se is a certain threshold value of wing loading. Sustained flights start roughly half-way to maturity and correlate with the emergence of the above mentioned plateau on the growth curves. The flight abilities improve together with aerodynamic characteristics of the wing: duration of flight increases, beat frequency decreases, but beat power increases etc.